1. Field of the Invention
The present invention relates to a sound image control apparatus and sound image control method for reproducing a transmission characteristic using a digital filter and convolving the transmission characteristic in an original sound (hereinafter, referred to as a source sound), and thereby controlling sound image localization.
2. Description of Related Art
There is a sound image control apparatus which uses a fact that the transmission characteristic changes due to influence of the shape of head and auricles according to the direction of a sound source position when a human catches a sound, reproduces a transmission characteristic using a digital filter and convolves the transmission characteristic in a source sound, and thereby controls sound image localization.
For example, Patent Document 1 (Japanese Patent Application Laid-Open No. H07-298399) discloses a stereophonic sound listening device holding transmission filters at intervals corresponding to a sound discrimination limit of a human when sound wave transmission characteristics of arrival sounds in respective directions around a head of a listener are reproduced.
FIG. 1 is a block diagram illustrating a configuration of a conventional sound image control apparatus.
In FIG. 1, sound image control apparatus 10 is configured with sound image control section 11, virtual sound field 1 sound image localization section 12, virtual sound field 2 sound image localization section 13, Panning Gain control section 14, virtual reflected sound generating section 15 and localized sound/virtual reflected sound adding section 16.
Panning Gain control section 14 is configured with virtual sound field 1 Rch Panning Gain control section 21, virtual sound field 1 Lch Panning Gain control section 22, virtual sound field 2 Rch Panning Gain control section 23, and virtual sound field 2 Lch Panning Gain control section 24, and localized sound/virtual reflected sound adding section 16 is configured with Rch localized sound/virtual reflected sound adder 25 and Lch localized sound/virtual reflected sound adder 26.
Virtual sound field 1 sound image localization section 12 and virtual sound field 2 sound image localization section 13 control localization to be in an arbitrary position mainly using a transmission characteristic filter (data).
Panning Gain control section 14 performs cross-fade processing on audio signals outputted from virtual sound field 1 sound image localization section 12 and virtual sound field 2 sound image localization section 13.
Sound image control apparatus 10 receives monaural input audio signal 30 as input, and outputs Rch output audio signal 31 and Lch output audio signal 32. Further, “41” is a transmission characteristic filter transfer system to virtual sound field 1 sound image localization section 12, and “42” is a transmission characteristic filter transfer system to virtual sound field 2 sound image localization section 13.
Sound image control section 11 outputs virtual sound field 1 Panning Gain control section control signal 43 to virtual sound field 1 Rch Panning Gain control section 21 and virtual sound field 1 Lch Panning Gain control section 22, and further outputs virtual sound field 2 Panning Gain control section control signal 44 to virtual sound field 2 Rch Panning Gain control section 23 and virtual sound field 2 Lch Panning Gain control section 24.
Virtual sound field 1 Rch Panning Gain control section 21, virtual sound field 1 Lch Panning Gain control section 22, virtual sound field 2 Rch Panning Gain control section 23 and virtual sound field 2 Lch Panning Gain control section 24 are controlled in gain by virtual sound field 1 Panning Gain control section control signal 43 and virtual sound field 2 Panning Gain control section control signal 44, and respectively output virtual sound field 1 Rch Panning Gain control section audio signal 45, virtual sound field 1 Lch Panning Gain control section audio signal 46, virtual sound field 2 Rch Panning Gain control section audio signal 47 and virtual sound field 2 Lch Panning Gain control section audio signal 48 to Rch localized sound/virtual reflected sound adder 25 and Lch localized sound/virtual reflected sound adder 26.
Further, virtual reflected sound generating section 15 outputs virtual reflected sound generating section Rch output audio signal 49 and virtual reflected sound generating section Lch output audio signal 50 to Rch localized sound/virtual reflected sound adder 25 and Lch localized sound/virtual reflected sound adder 26, respectively.
Rch localized sound/virtual reflected sound adder 25 adds virtual sound field 1 Rch Panning Gain control section audio signal 45, virtual sound field 2 Rch Panning Gain control section audio signal 47 and virtual reflected sound generating section Rch output audio signal 49, and outputs the result as Rch output audio signal 31.
Lch localized sound/virtual reflected sound adder 26 adds virtual sound field 1 Lch Panning Gain control section audio signal 46, virtual sound field 2 Lch Panning Gain control section audio signal 48 and virtual reflected sound generating section Lch output audio signal 50, and outputs the result as Lch output audio signal 32.
According to the above-described configuration, it is necessary to have transmission characteristic filters at fixed intervals. In order to obtain sound image localization with higher accuracy, it is necessary to have transmission characteristic filters in a larger number of directions, and therefore large amounts of storage areas are required to store a large number of transmission characteristic filters. The apparatus of Patent Document 1 intends to realize the sound image localization with higher accuracy without increasing the data amount so much by preparing the transmission characteristic filters at only intervals corresponding to the sound discrimination limit of a human.
In such a conventional sound image control apparatus, it is expected to reduce the data amount to some extent, but transmission characteristic filters are not prepared at fixed intervals, and therefore the control method becomes complicated when selecting a transmission characteristic filter in the vicinity of a coordinate point of a move destination calculated from a move instruction for controlling the sound image, and there is a problem that the circuit scale of the sound image control section for controlling the sound image increases, and the operation amount increases.
Further, for the distance direction, it is necessary to prepare transmission characteristic filters in all directions for each distance, and therefore, in order to increase the accuracy in the distance direction, transmission characteristic filters corresponding to all directions are required for one distance and there is a problem that an enormous amount of transmission characteristic filters are required.